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Copyright © 2009 Pearson Education, Inc.
PowerPoint Lectures for
Biology: Concepts & Connections, Sixth Edition
Campbell, Reece, Taylor, Simon, and Dickey
Chapter 21 Nutrition and Digestion
Lecture by Edward J. Zalisko
Copyright © 2009 Pearson Education, Inc.
Introduction: Getting Their Fill of Krill
A 72-ton humpback whale eats small fishes and crustaceans called krill
A whale’s digestive system may process up to 2 tons of krill a day
Copyright © 2009 Pearson Education, Inc.
Humpback whales strain krill from seawater using large plates, called baleen
– Whales take a large gulp of water into their throat
– As they force water out, it is strained through baleen plates that hang from the upper jaw
Humpback whales create a net of bubbles to concentrate the krill
Introduction: Getting Their Fill of Krill
Copyright © 2009 Pearson Education, Inc.
21.1 Animals ingest their food in a variety of ways
Most animals have one of three kinds of diets
– Herbivores, plant-eaters—cattle, snails, sea urchins
– Carnivores, meat-eaters—lions, hawks, spiders
– Omnivores, eating both plants and other animals—humans, roaches, raccoons, crows
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Animals obtain and ingest their food in different ways
– Suspension feeding
– Substrate feeding
– Fluid feeding
– Bulk feeding
Video: Hydra Eating Daphnia
Video: Lobster Mouth Parts
Video: Shark Eating a Seal
21.1 Animals ingest their food in a variety of ways
Copyright © 2009 Pearson Education, Inc.
21.2 Overview: Food processing occurs in four stages
Food is processed in four stages
– Ingestion
– Digestion
– Absorption
– Elimination
Mechanicaldigestion
Piecesof food
Food
Chemical digestion(hydrolysis)
Nutrientmoleculesenter bodycells
Smallmolecules
Undigestedmaterial
DigestionIngestion 21 Absorption3 Elimination4
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Mechanical digestion breaks food down into smaller pieces
– Smaller pieces are easier to swallow
– Smaller pieces have more surface area exposed to digestive fluids
21.2 Overview: Food processing occurs in four stages
Copyright © 2009 Pearson Education, Inc.
Chemical digestion breaks down large organic molecules into their components
– Proteins split into amino acids
– Polysaccharides and disaccharides into monosaccharides
– Nucleic acids into nucleotides
21.2 Overview: Food processing occurs in four stages
Protein-digestingenzymes
Polysaccharide
Macromolecule
Protein
Carbohydrate-digestingenzymes
Components
Amino acids
MonosaccharidesDisaccharide
Nucleic acid-digestingenzymes
NucleotidesNucleic acid
Fat-digestingenzymes
Fat Glycerol Fatty acids
Copyright © 2009 Pearson Education, Inc.
21.3 Digestion occurs in specialized compartments
Sponges digest food in vacuoles
Most animals digest food in compartments
– Enzymes break down the food
– Food particles move into cells lining the compartment
– Undigested materials are expelled
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Cnidarians and flatworms have a gastrovascular cavity with a single opening, the mouth
– Food enters the mouth
– Undigested food is expelled back out the mouth
21.3 Digestion occurs in specialized compartments
Food(Daphnia,a waterflea)
Gastrovascularcavity
Food particleengulfed
Soft tissuesdigested
Tentacle
Mouth
Digestiveenzymesreleased froma gland cell
Food particledigested infood vacuole
4
3
2
1
Copyright © 2009 Pearson Education, Inc.
Most animals have an alimentary canal with
– Mouth
– Anus
– Specialized regions
21.3 Digestion occurs in specialized compartments
Mouth
Pharynx
Esophagus
Crop
Gizzard Anus
Intestine
EarthwormDorsal fold
Interior of intestine
Esophagus
Wall of intestine
Midgut
Mouth
Crop
Grasshopper
Anus
HindgutGastric pouches
Mouth
Esophagus
Crop
Gizzard
Anus
Intestine
Bird
Stomach
Mouth
Pharynx
Esophagus
Crop
Gizzard Anus
Intestine
Earthworm
Dorsal fold
Interior of intestine
Wall of intestine
Copyright © 2009 Pearson Education, Inc.
21.4 The human digestive system consists of an alimentary canal and accessory glands
Alternating waves of contraction and relaxation by smooth muscle in the walls of the canal move food along in a process called peristalsis
Sphincters control the movement of food into and out of digestive chambers
Copyright © 2009 Pearson Education, Inc.
The pyloric sphincter
– Regulates the passage of food from the stomach to the small intestine
– Limits the upward movement of acids into the esophagus
21.4 The human digestive system consists of an alimentary canal and accessory glands
Pharynx
Esophagus
Mouth
Oralcavity
Tongue
Mouth
Salivaryglands
Salivaryglands
Esophagus
Gall-bladder
Liver
Pancreas Gall-bladder
Liver
Pancreas
Smallintestine
Stomach
Rectum
Anus
Largeintestine
Smallintestine
Rectum
Anus
Largeintestine
Esophagus
Stomach
Smallintestine
Sphincter
Sphincter
A schematic diagram of thehuman digestive system
Mouth Salivaryglands
Esophagus
Gall-bladder
Liver
Pancreas
Smallintestine
Stomach
Rectum
Anus
Largeintestine
A schematic diagram of thehuman digestive system
Pharynx
Esophagus
Oralcavity
Tongue
Mouth
Salivaryglands
Gall-bladder
Liver
Pancreas
Smallintestine
Rectum
Anus
Largeintestine
Esophagus
Stomach
Smallintestine
Sphincter
Sphincter
Copyright © 2009 Pearson Education, Inc.
21.5 Digestion begins in the oral cavity
Teeth break up food, saliva moistens it
– Salivary enzymes begin the hydrolysis of starch
– Buffers neutralize acids
– Antibacterial agents kills some bacteria ingested with food
The tongue tastes, shapes the bolus of food, and moves it toward the pharynx
Opening of asalivary gland duct
Salivaryglands
Tongue
Incisors
Premolars
Molars
“Wisdom”tooth
Teeth
Canine
Copyright © 2009 Pearson Education, Inc.
21.6 After swallowing, peristalsis moves food through the esophagus to the stomach
The trachea conducts air to the lungs
The esophagus conducts food from the pharynx to the stomach
Epiglottisup
Pharynx
Esophagealsphincter
Bolus offood
Tongue
Esophagus
Larynx
Trachea
Sphincter contracted
Epiglottisup
Pharynx
Esophagealsphincter
Bolus offood
Tongue
Esophagus
Larynx
Trachea
Sphincter contracted
Epiglottisdown
Esophagus
Larynxup
Sphincter relaxed
Epiglottisup
Pharynx
Esophagealsphincter
Bolus offood
Tongue
Esophagus
Larynx
Trachea
Sphincter contracted
Epiglottisdown
Esophagus
Larynxup
Sphincter relaxed
Epiglottisup
Sphincter contracted
Larynxdown
Copyright © 2009 Pearson Education, Inc.
The swallowing reflex
– Food moves from the pharynx into the esophagus
– The swallowing reflex prevents food from entering the trachea
– A coughing reflex helps expel materials that accidentally enter the trachea
21.6 After swallowing, peristalsis moves food through the esophagus to the stomach
Esophageal sphincter(contracted)
Bolus offood
Muscles contract,constricting passagewayand pushing bolus down
Stomach
Bolus offood
Muscles relax,allowing passagewayto open
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21.7 CONNECTION: The Heimlich maneuver can save lives
The Heimlich maneuver can dislodge food from the pharynx or trachea during choking
Brain damage will occur within minutes if no airway is open
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21.8 The stomach stores food and breaks it down with acid and enzymes
Acid
– pH 2
– Parietal cells secrete hydrogen and chloride ions, which combine to make HCl
– Acid kills bacteria and breaks apart cells in food
Pepsinogen and HCl produce pepsin
– Pepsin production activates more pepsinogen production—positive feedback
– Pepsin begins the chemical digestion of proteins
– Acidic gastric juices mix with food to produce acid chyme
Copyright © 2009 Pearson Education, Inc.
What prevents the gastric juices from digesting the walls of the stomach?
– Mucus helps protect against HCl and pepsin
– New cells lining the stomach are produced about every 3 days
21.8 The stomach stores food and breaks it down with acid and enzymes
Interior surface
of stomach
Lumen (cavity)
of stomachStomach Gastrin
Esophagus
Sphincter
Sphincter
Small
intestine
Pits
Release of gastric juice
(mucus, HCl, and pepsinogen)
Epithelium
Gastric
gland
Mucous
cells
Chief cells
Parietal cells
Pepsin
(active
enzyme)
3
Pepsinogen
H+
Cl–
HCl
2
1
Interior surfaceof stomach
Lumen (cavity)of stomach
Stomach Gastrin
Esophagus
Sphincter
Sphincter
Smallintestine
Interior surface
of stomach
Pits
Release of gastric juice(mucus, HCl, and pepsinogen)
Epithelium
Gastric
gland
Mucous
cells
Chief cells
Parietal cells
Pepsin(activeenzyme)
Pepsinogen
H+
Cl–
HCl
2
3
1
Copyright © 2009 Pearson Education, Inc.
21.9 CONNECTION: Digestive ailments include acid reflux and gastric ulcers
Acid reflux into esophagus—heartburn and GERD
Bacterial infections (Helicobacter pylori) in the stomach and duodenum can produce ulcers
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21.10 The small intestine is the major organ of chemical digestion and nutrient absorption
Small intestine is named for its smaller diameter—it is about 6 meters long
Alkaline pancreatic juice neutralizes acid chyme and its enzymes digest food
Bile, made in the liver and stored in the gall bladder, emulsifies fat for attack by pancreatic enzymes
Gall-bladder
Pancreatic juice
Liver Bile
Acid chyme
Pancreas
Stomach
Intestinalenzymes
Duodenum ofsmall intestine
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Enzymes from cells of the intestine continue digestion
21.10 The small intestine is the major organ of chemical digestion and nutrient absorption
Copyright © 2009 Pearson Education, Inc.
Surface area for absorption is increased by
– Folds of the intestinal lining
– Fingerlike villi
21.10 The small intestine is the major organ of chemical digestion and nutrient absorption
Musclelayers
Largecircular folds
Villi
Lumen
Nutrientabsorption
Intestinal wall
Lymphvessel
Bloodcapillaries
Villi
Nutrientabsorption
Epithelialcells
Lumen of intestineVeinwith blooden route tothe liver
Lumen of intestine
Nutrient absorptioninto epithelial cells
Microvilli
Aminoacidsand
sugars
Fats
Blood
Fattyacidsand
glycerol
Epithelial cellslining villus
Lymph
Musclelayers
Largecircular folds
Villi
Lumen
Nutrientabsorption
Intestinal wall
Veinwith blooden route tothe liver
Copyright © 2009 Pearson Education, Inc.
Nutrients pass across the epithelium and into blood
Blood flows to the liver where nutrients are processed and stored
21.10 The small intestine is the major organ of chemical digestion and nutrient absorption
Lymphvessel
Bloodcapillaries
Villi
Nutrientabsorption
Epithelialcells
Lumen of intestine Lumen of intestine
Nutrient absorptioninto epithelial cells
Microvilli
Aminoacidsand
sugars
Fats
Blood
Fattyacidsand
glycerol
Epithelial cellslining villus
Lymph
Copyright © 2009 Pearson Education, Inc.
21.11 One of the liver’s many functions is processing nutrient-laden blood from the intestines
Blood from the digestive tract drains to the liver
The liver performs many functions
– Glucose in blood is converted to glycogen and stored in the liver
– Liver synthesizes many proteins including blood clotting proteins and lipoproteins that transport fats and cholesterol
– Liver changes toxins to less toxic forms
– Liver produces bile
Copyright © 2009 Pearson Education, Inc.
21.12 The large intestine reclaims water and compacts the feces
Diarrhea occurs when too little water is reclaimed
Constipation occurs when too much water is reclaimed
Feces are stored in the rectum
Colon bacteria produce vitamins—biotin, vitamin K, B vitamins
Copyright © 2009 Pearson Education, Inc.
Appendix
– Located near the junction of the small intestine and colon
– Makes a minor contribution to immunity
21.12 The large intestine reclaims water and compacts the feces
Large
intestine
(colon)
Endof smallintestine
Appendix
Cecum
Sphincter
Unabsorbed
food material
Anus
Rectum
Smallintestine
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21.13 EVOLUTION CONNECTION:Evolutionary adaptations of vertebrate digestive systems often relate to diet
The length of the digestive tract often correlates with diet
– Herbivores and omnivores have relatively longer digestive tracts than carnivores
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Many herbivores have specializations of the gut that promote the growth of cellulose-digesting microbes
– Rumen
– Reticulum
– Omasum
– Abomasum
21.13 EVOLUTION CONNECTION:Evolutionary adaptations of vertebrate digestive systems often relate to diet
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21.14 Overview: A healthy diet satisfies three
needs
Fuel to power the body
Organic molecules to build molecules
Essential nutrients—raw materials that animals cannot make for themselves
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21.15 Chemical energy powers the body
Nutrients are oxidized inside cells to make ATP
ATP is the main energy “currency” in a cell
Proteins, carbohydrates, and fats are the main sources of dietary calories
– A gram of fat has more than twice as many calories as a gram of carbohydrate or protein
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Basal metabolic rate (BMR) is the energy a resting animal requires each day
Metabolic rate is the BMR plus the energy needed for physical activity
Excess energy is stored as glycogen or fat
21.15 Chemical energy powers the body
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Our metabolic rates typically decrease throughout adulthood
An active life burns more calories
21.15 Chemical energy powers the body
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21.16 An animal’s diet must supply essential
nutrients
Essential nutrients cannot be made from any raw material
Undernourishment—not enough calories
Malnourishment—missing essential nutrients
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Animals cannot produce eight of the 20 amino acids
These eight amino acids are essential amino acids
These eight amino acids must come from the diet
21.16 An animal’s diet must supply essential
nutrients
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21.17 CONNECTION: Vegetarians must be sure to obtain all eight essential amino acids
The eight essential amino acids can be obtained from
– Animal protein
– The proper combination of plant foods
Beans and
other
legumes
Essential
amino acids
Corn
Methionine
Valine
(Histidine)
Threonine
Phenylalanine
Leucine
Isoleucine
Tryptophan
Lysine
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21.18 A healthy diet includes 13 vitamins and many essential minerals
Essential vitamins and minerals
– Required in minute amounts
– Extreme excesses can be dangerous
– Excess water-soluble vitamins can be eliminated in urine
– Excess fat-soluble vitamins can accumulate to dangerous levels in body fat
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Minerals are simple inorganic nutrients usually required in small amounts
– Calcium and phosphorus are required in larger amounts
– Most people ingest more salt than they need
21.18 A healthy diet includes 13 vitamins and many essential minerals
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21.19 CONNECTION: Do you need to take vitamin and mineral supplements?
Recommended Dietary Allowances (RDAs) are debated
Excessive doses of vitamin A and iron can be dangerous
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Extra doses of some vitamins are recommended by the USDA
– Extra B12 for people over 50
– Extra vitamin D for people with dark skin or who get little sun
21.19 CONNECTION: Do you need to take vitamin and mineral supplements?
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21.20 CONNECTION: What do food labels tell us?
Food labels indicate
– Serving size
– Calories per serving
– Amounts of selected nutrients per serving and as a percentage of daily value
– Recommendations for daily limits of selected nutrients
Ingredients: wholewheat flour, water,high fructose cornsyrup, wheat gluten,soybean or canolaoil, molasses, yeast,salt, cultured whey,vinegar, soy flour,calcium sulfate(source of calcium).
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21.21 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past
Overnourishment: consuming more food energy than is needed
World Health Organization recognizes obesity as a major global health problem
Of people in the United States
– 30% are obese
– 35% are overweight
– 15% of children and adolescents are overweight
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Obesity leads to
– Diabetes
– Cancer
– Cardiovascular disease
– 300,000 deaths per year in the United States
21.21 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past
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Leptin
– Produced by fat cells
– Suppresses appetite
– High levels in humans do not suppress appetite
– May be adaptive in humans to prevent excessive weight loss
21.21 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past
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Leptin-deficient mice were very obese
After treatment with leptin, leptin-deficient mice lost weight
Obese leptin-deficient children lose weight with leptin treatment
Adults with healthy leptin genes do not lose weight with leptin treatments
21.21 EVOLUTION CONNECTION: The human health problem of obesity may reflect our evolutionary past
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21.22 CONNECTION: What are the health risks and benefits of weight loss plans?
Weight loss diets
– May help individuals lose weight
– May have health risks leading to malnourishment
Diets fail because people return to old eating habits
The most effective diets combine
– Increased exercise
– Limited balanced diet of about 1200 calories per day
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21.23 CONNECTION: Diet can influence cardiovascular disease and cancer
A healthy diet may reduce the risk of
– Cardiovascular disease
– Cancer
Two main types of cholesterol
– LDL—contributes to blocked blood vessels and higher blood pressure
– HDL—tends to reduce blocked blood vessels
– Exercise increases HDL levels
– Smoking decreases HDL levels
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The relationship between food and health is complex
The American Cancer Society recommends
– Regular exercise
– A diverse diet of healthy foods with an emphasis on plant sources
21.23 CONNECTION: Diet can influence cardiovascular disease and cancer
A healthydiet
satisfies three needs
(a)
coenzymes,ion balances,
nerve functions,bone structure
proteindeficiency
essentialfatty acids
moleculesof cells
(f)
(e)
(c)(b)
(d)
undernourishment
(g)
needed to build
which include
too muchleads to
not enoughleads to
lackresults in
have manyfunctions,such as
lackproducesmost
common is
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You should now be able to
1. Describe the four stages of food processing
2. Describe the main components of the human digestive tract and their functions
3. Explain how teeth and saliva help us swallow
4. Describe the Heimlich maneuver
5. Explain why the stomach does not digest itself
6. Describe the causes and treatment of heartburn, GERD, and gastric ulcers
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7. Compare the structures and functions of the small and large intestines
8. Compare the digestive tracts of carnivores and herbivores
9. Distinguish between undernourishment and malnourishment
10. Describe the types of information found on food labels
11. Explain how a healthy diet and exercise promote good health
You should now be able to